You would need to insert the logo in each report, one by one, since you will need to assign the space that will be used and either move/remove elements to make the space.
If you are using the default forms, most use the web-interface layout designer, so you would edit the layout there. Adding is fairly simple
1. Create the layout grid space to receive your logo,
2. Click on the Insert/Image button and browse to select your image file from your computer. This will upload the file to BI.
2a. You can also use the URL link IF the image is found at a web-accessible URL (http:\\...) You cannot use a server\file reference here.
3. Once inserted you can resize the image smaller if need be.
4. Save and repeat on the other form/report layouts.